Introduction:

One of the most abundant and ubiquitous groups of nongame fishes found in Minnesota is the darter group (Percidae: Etheostomatini). These lively and colorful fishes inhabit nearly all of our streams and rivers and many of our lakes. We know in general that darters play an important role in the trophic structure of stream ecosystems, and we know that some species are important indicators of general water quality. Yet, we know very little about the specific life histories of the darters of our state, and we know even less about how their resource utilization patterns change with changes in habitat and community structure.

To date, only three life history studies have been cared out on Minnesota darter populations. Erickson (1977) studied the banded darter (Etheostoma zonale) in the Cannon River; Coon (1982) studied several aspects of the comparative ecology of the rainbow (E. coeruleum), fantail (E. flabellare) and Johnny (E. nigrum) darters in the Root River; and Hatch (1982, 1986) studied the gilt darter (Percina evides) in the St. Croix River drainage. Information about food habits of logperch (P. caprodes) from Lake Vermilion and of Iowa (E. exile) and Johnny darters from Long Lake has been reported by Dobie (1959) and Moyle (1969), respectively.

In order to fill in some of the gaps in our knowledge of darter natural history, a series of studies funded by the Nongame Wildlife Program of the Minnesota Department of Natural Resources was begun in 1983 to elucidate the life histories of all fifteen Minnesota darter species. The approach has been to intensively study different but overlapping assemblages of darter species in geographically disjunct and physically diverse drainages.

What follows constitutes the final report of the first of these studies, which centered on the darters of the St. Croix River drainage upstream of the St. Croix Dalles. The specific objectives of the this study were: 1) to determine growth rates, length-weight relationships, fecundities, and fecundity relationships to length, weight, and age for populations of Etheostoma nigrum, Percina caprodes, P. maculata, and P. phoxocephala from the Sunrise River, Chisago County, Minnesota; 2) to summarize microhabitat data and estimate the spawning period of the above species; and 3) to elucidate food utilization patterns of the above species and P. evides at riffles in the Sunrise and St. Croix rivers.